In pump probe spectroscopy shot to shot detection is the ideal method of acquiring data as it takes advantage of the strong intensity correlations that exist between laser pulses that are close together in time. The further apart the pulses are in time, the worse the correlations become, and as a result, the data becomes noisier. Shot to shot differencing has been widely used at normal laser repetition rates (i.e., a few kHz), but becomes much more difficult at higher repetition rates. The primary reason for this is that the “pump” laser beam needs to be modulated (i.e., blocked) at exactly half the repetition rate of the “probe” laser beam. At slow laser repetition rates (˜5 kHz or lower), this can be done with a mechanical chopper. At higher repetition rates (e.g., 100 kHz), however, the moment of inertia of the spinning chopper blade becomes sufficiently high that it is challenging for the blade to be synchronized to the laser output pulse train.